The external oblique has been partially removed below its costal origins. The lower posterior part of the muscle has been dissected to display muscular branches of the twelfth thoracic nerve (subcostal n.) which enter the muscle from its internal aspect. Fascia between the external and internal oblique muscles have been preserved.

1
.

Rib XII

2
.

Rib XI

3
.

External oblique muscle (origin)

4
.

Costal cartilage X

5
.

Lateral cutaneous branch intercostal nerve XI

6
.

Posterior branches intercostal artery XI

7
.

Internal oblique muscle (covered by fascia)

8
.

Lateral cutaneous branch thoracic nerve XII (subcostal nerve)

9
.

Muscular branches thoracic nerve XII

10
.

External oblique muscle (cut across and reflected)

11
.

Latissimus dorsi muscle (cut across)

12
.

Thoracolumbar fascia

13
.

Dorsal branch thoracic nerve XII (lateral branch)

14
.

Aponeurosis of latissimus dorsi (in this specimen aponeurosis overlaps posterior border of external oblique muscle so that there is no lumbar triangle)